1. Field of the Invention
This invention relates to sources of driving power for mechanical loads and, more specifically, to hybrid-drive vehicles.
2. Prior Art
With the advent of the shortage of oil and the rapidly escalating price of it, associated with the economic and international dangers with which this deplorable situation has confronted the world, new types of transportation systems have been proposed. Amongst these is advocated the widespread use of electric cars, since these can utilize any type of fuel, wind, solar, synthetic fuels, coal, water power, hydrogen and nuclear power, for example. Anything that can be used to generate electricity can provide power for electric vehicles. Unfortunately batteries now and in the forseeable future are too heavy to provide much range or performance for electric vehicles. To rectify this situation, the United States Department of Energy has proposed that hybrid vehicles (battery-powered drive train plus a heat-engine-powered drive train), be the interim solution. There are two types of such vehicles, the first being a series hybrid, of which the diesel-electric locomotive is an example. In the series hybrid, a heat engine, usually of the internal combustion type, drives the electric generator powering the electric motors coupled to the wheels. The generator is, in actuality, an electric transmission. The other type is the parallel hybrid in which there is a battery-pack-powered electric drive coupled to the wheels, and in addition there is a heat engine, usually of the internal combustion type, also coupled to the wheels. Usually both drives in a parallel hybrid are coupled to the same set of wheels, but it is possible to have one drive coupled to one set of wheels and the other coupled to another set. When the electric drive is operating in a parallel hybrid, it is desirable to disconnect the heat engine when it is not being used, to avoid high friction losses. On the other hand when the heat engine alone is operating the vehicle, it is not necessary to disconnect the electric drive motor's rotor, since the friction loss is small, and it has the advantage of acting as a flywheel.
Such exhalted scientific organizations as Jet Propulsion Laboratory and its parent, the National Aeronautics and Space Administration, have dismissed the idea of a series hybrid as being too inefficient. To quote Briggs & Stratton engineers, who have developed an effective hybrid using their small 18 horsepower engine, "the first--and simplest--method (to build a hybrid) is to add an engine-driven generator to the electric motor to recharge its batteries. This design adds nothing to the electric motor's performance, only its range, and suffers significant mechanical-electrical-mechanical conversion losses. In short, the series approach is deemed by engineers to be an inefficient one."
The same argument has been used by JPL engineers to describe the use of an electric generator to drive the electric motor as is done with the diesel-electric locomotive. Another detracting argument is that such a generator would be much too heavy for an automobile. Earnest H. Wakefield, in his book, The Consumer's Electric Car, states that a series wound electric motor is capable of being used as a transmission without gearing because of its ability to increase its torque by the square of the current increase. Thus, an electric transmission (or series hybrid) can be more efficient than a standard transmission at lower speed range by reducing the large low speed losses. To a lesser extent this argument holds true with a shunt wound motor or even a conventional permanent magnet motor. Even JPL and Briggs & Stratton agree that the electric motor can be an effective and efficient method to start an automobile, especially if it is a series wound D.C. motor. Briggs & Stratton is quoted as saying its "hybrid gasoline-electric powered car takes advantage of the complementary characteristics of its two powerplants--the low speed power of the electric motor and the high speed performance of the gasoline engine." So we have a complementary situation. A series hybrid would be very useful and efficient in low speed city driving, while a parallel hybrid engine with a 1:1 gear ratio to the differential can perform efficiently at the higher speeds.
In overcoming the initial inertia of rest of a vehicle or other load it would be desirable to add the rectified current from an engine driven alternator to that from the battery pack, applying the sum to the electrical drive motor. With conventional alternator structure there is much elemental iron in the magnetic circuit of the alternator and passing the current from the battery pack to the motor thru the alternator would be unthinkable since the iron would saturate, causing a loss of output current from the alternator. The alternator would become merely a load.
Therefore, it is an object of this invention to overcome the general disadvantages set forth hereinbefore.
It is a further object of this invention to provide an improved hybrid electrical-heat engine drive for a mechanical load.
It is an additional object of this invention to provide an electrical drive system which provides, selectively, high torque for a desired period of time.